A seamless tube or pipe, which is normally used in a telescoping tube coupling, is generally round at both of its interior and exterior. However, in the case of welded tubes or pipes, the interior is sometimes out of round because of a trace of a welding bead left thereon. With a welded tube or pipe, therefore, a coupling which operates upon the interior of one of the tubes or pipes is undesirable.
With telescoping tubes or pipes, it is desirable that the interior of the outer tube and the exterior of the inner tube be as close as possible in size to facilitate secure coupling.
A coupling device for a telescoping tube arrangement should meet the requirements that (1) the coupling does not scratch the tubes being coupled, (2) no noises are generated by the coupling at the time that the tubes are telescoped into or out of each other, and (3) the coupling accurately and firmly stops relative axial shifting and relative tangential rotation of the coupled tubes using a comparatively small force.